Osmometry is one of the few absolute molecular weight techniques used in the characterization of polymers. In the case of membrane osmometry, a semipermeable membrane can be used to separate a polymer solution from its solvent phase. The difference in chemical potential between the solution and the solvent causes the solvent to diffuse through the semipermeable membrane to the solution side of the membrane, until a static pressure difference, the so-called osmotic pressure, is established to counter-balance the chemical potential difference. The magnitude of the osmotic pressure is proportional to the number of polymer molecules present in the solution, and, therefore, provides a measure of the number-average molecular weight of the polymer. Most commercially available osmometers involve difficult measurements and long periods of time to reach osmotic equilibrium.